The NIH-HSCF has routinely grown hES cells on the NIH registry from August 2003. In the following year, most of the hES cells on the NIH registry were obtained, expanded in culture and analyzed by karyotype and FACS analysis. In the period to 8/2004, the central achievement of NIH-HSCF was to show that sub-clones of a hES cell line had a stable genome using a high-resolution genome scanning method. This result provides the convincing evidence that hES cells can be grown for long periods without genetic change. In the most recent reporting period to 8/05, the major focus has been to use the skills of the staff in the facility to develop general standards to assess many hES cell lines. This work is an international collaboration organized through the International Stem Cell Consortium. The ISCC is sponsored by the International Stem Cell Forum, a grouping of research agencies in several countries including Australia, Canada, Israel, Sweden, the United Kingdom and the United States. The ISCC has developed a set of standard antibodies and a gene array to probe the differentiated state of hES cells. The ISCC is also promoting a careful analysis of the safety of hES cell lines. The NIH-HSCF was one of the few sites contributing multiple hES cells from different providers grown under standard conditions. In the period to 8/06 two approaches were developed to measure stress responses in hES cells. This goal was pursued because activated stress response pathways were considered to be the most likely source of the technical difficulty growing hES cells. In the period to 8/07 these stress response measures have been used to generate simple quantitative tests that measure the growth state of hES colonies. These tools are being used to optimize growth conditions for undifferentiated hES cells. This information and gene expression data on different hES cell lines is accessible on the NIH Stem Cell Facility web site.